The macOS system must be configured with dedicated user accounts to decrypt the hard disk upon startup.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-230762	APPL-11-000032	SV-230762r802378_rule		Medium

Description
When "FileVault" and Multifactor Authentication are configured on the operating system, a dedicated user must be configured to ensure that the implemented Multifactor Authentication rules are enforced. If a dedicated user is not configured to decrypt the hard disk upon startup, the system will allow a user to bypass Multifactor Authentication rules during initial startup and first login.

STIG	Date
Apple macOS 11 (Big Sur) Security Technical Implementation Guide	2021-11-19

Details

Check Text ( C-33707r802376_chk )
Retrieve a list of authorized FileVault users: $ sudo fdesetup list fvuser,85F41F44-22B3-6CB7-85A1-BCC2EA2B887A If any unauthorized users are listed, this is a finding. Verify that the shell for authorized FileVault users is set to “/usr/bin/false”, which prevents console logins: $ sudo dscl . read /Users/ UserShell UserShell: /usr/bin/false If the FileVault users' shell is not set to "/usr/bin/false", this is a finding.

Check Text ( C-33707r802376_chk )

Retrieve a list of authorized FileVault users:
$ sudo fdesetup list

fvuser,85F41F44-22B3-6CB7-85A1-BCC2EA2B887A

If any unauthorized users are listed, this is a finding.

Verify that the shell for authorized FileVault users is set to “/usr/bin/false”, which prevents console logins:
$ sudo dscl . read /Users/ UserShell

UserShell: /usr/bin/false

If the FileVault users' shell is not set to "/usr/bin/false", this is a finding.

Fix Text (F-33680r802377_fix)
Note: In previous versions of macOS, this setting was implemented differently. Systems that used the previous method should prepare the system for the new method by creating a new unlock user, verifying its ability to unlock FileVault after reboot, then deleting the old FileVault unlock user. Disable the login ability of the newly created user account: $ sudo /usr/bin/dscl . change /Users/ UserShell /usr/bin/false Remove all FileVault login access from each user account defined on the system that is not a designated FileVault user: $ sudo fdesetup remove -user

Fix Text (F-33680r802377_fix)

Note: In previous versions of macOS, this setting was implemented differently. Systems that used the previous method should prepare the system for the new method by creating a new unlock user, verifying its ability to unlock FileVault after reboot, then deleting the old FileVault unlock user.

Disable the login ability of the newly created user account:
$ sudo /usr/bin/dscl . change /Users/ UserShell /usr/bin/false

Remove all FileVault login access from each user account defined on the system that is not a designated FileVault user:
$ sudo fdesetup remove -user